Hybrid surface magnet machine

ABSTRACT

A hybrid electrical machine containing surface mounted magnets which includes a magnetically permeable cylindrically shaped stator assembly having at least one stator winding formed about a plurality of stator teeth, a rotor assembly concentrically disposed within the stator assembly, including a magnetically permeable rotor backiron, a rotational drive mechanism coupled to the rotor backiron, and a plurality of protruding rotor poles, each including a magnetically permeable pole support assembly, a winding provided around the pole support assembly, and a radially magnetized permanent magnet assembly disposed about the pole support assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. patent application is a continuation of U.S. patentapplication Ser. No. 14/668,367, filed Mar. 25, 2015, which is relatedto and claims the priority benefit of U.S. Provisional PatentApplication Ser. No. 61/969,894, filed Mar. 25, 2014, the contents ofwhich are hereby incorporated by reference in their entirety into thepresent disclosure.

STATEMENT REGARDING GOVERNMENT FUNDING

This invention was made with government support under N00014-12-1-1020awarded by the Office of Naval Research. The government has certainrights in the invention.

TECHNICAL FIELD

The present invention generally relates to electric machines andparticularly to hybrid electrical machines with permanent magnets andfield windings.

BACKGROUND

This section introduces aspects that may help facilitate a betterunderstanding of the disclosure. Accordingly, these statements are to beread in this light and are not to be understood as admissions about whatis or is not prior art.

A typical approach to power generation includes use of a wound rotorsynchronous machine (WRSM) which can be used for voltage regulation. Thesame machine may be used as a motor, containing increased flexibilityassociated to a secondary winding which may be used to regulate outputtorque. Another type of machine is a permanent magnet synchronousmachine (PMSM), which typically offers lower loss and higher powerdensities.

Referring to FIG. 1, a cross-sectional schematic of an example topologyfor a hybrid machine is shown. The hybrid machine 1 includes a statorassembly 2 and a rotor assembly 3. The stator assembly 2 includes astator backiron 4 while the rotor assembly 3 includes a rotor backiron5. The stator assembly 2 further includes a winding 6, configured toprovide a magnetomotive force applicable on the rotor assembly 3. Therotor assembly 3 includes a winding 7 and one or more permanent magnets8 which together generate a magnetomotive force applicable on the statorassembly 3 which together with the magnetomotive force generated by thestator assembly cause rotation of the rotor assembly 3. The statorassembly 2 and the rotor assembly 3 are radially separated by an air gap12. The flux produced from the rotor assembly 3 may be approximatelymodeled using a series circuit configuration depicted in FIG. 1 in acutout spanning the rotor assembly 3 and the stator assembly 2. Based onthe model, a combination of two sources identified as F_(fd) and F_(pm),referring to field windings and permanent magnet magnetomotive force,coupled to each other in series, are connected to a further tworeluctances

_(pm) and

_(g), referring to the permanent magnet and air gap, connected to thetwo supplies also in series. The magnetomotive force sources in themagnetic circuit, dissipated across the reluctances, produce a flux inthe air-gap (Φ_(g)), similar to current in an electric circuit comprisedof electromotive force sources (i.e. voltage) and resistances. Theseries combination is terminated at each end at a ground, representingthe stator backiron 4 and the rotor backiron 5.

Placement of magnets and field windings within the rotor is asignificant factor in the performance metrics of the hybrid machine, oneof which is the torque producing capability relative to the machine sizeor mass and for a given loss. While beneficial when compared to the massvs. loss characteristics of the WRSM, there are several limitationsinherent in the topology shown in FIG. 1.

Given prior machine configurations, the torques, powers, regulationcapability, and the achievable torque density associated therewith,there is unmet need for developing machines with improved torquedensity, power regulation capability, and lower mass for a given powerloss compared to machines of prior art.

SUMMARY

A hybrid electrical machine which includes surface mounted magnetsincludes a magnetically permeable cylindrically shaped stator assemblyhaving at least one stator winding formed about a plurality of statorteeth, a rotor assembly concentrically disposed within the statorassembly, including a magnetically permeable rotor backiron, arotational drive mechanism coupled to the rotor backiron, and aplurality of protruding rotor poles, each including a magneticallypermeable pole support assembly, a winding provided around the polesupport assembly, and a radially magnetized permanent magnet assemblydisposed about the pole support assembly.

An energy conversion system is also disclosed. The system includes amechanical arrangement configured to i) provide mechanical power in apower generation mode, and ii) receive mechanical power in a motoringmode, and a hybrid electrical machine which includes a magneticallypermeable cylindrically shaped stator assembly having at least onestator winding formed about a plurality of stator teeth, a rotorassembly concentrically disposed within the stator assembly, including amagnetically permeable rotor backiron, a rotational drive mechanismcoupled to the rotor backiron, and a plurality of protruding rotorpoles, each including a magnetically permeable pole support assembly, awinding provided around the pole support assembly, and a radiallymagnetized permanent magnet assembly disposed about the pole supportassembly. The mechanical arrangement is coupled to the rotational drivemechanism.

BRIEF DESCRIPTION OF DRAWINGS

Some of the figures shown herein may include dimensions. Further, someof the figures shown herein may have been created from scaled drawingsor from photographs that are scalable. It is understood that suchdimensions or the relative scaling within a figure are by way ofexample, and not to be construed as limiting.

FIG. 1 is a cross sectional view of a typical four-pole hybrid machineconfiguration found in the prior art.

FIG. 2a is a cross sectional schematic view of a hybrid machine with astator and rotor, according to the present disclosure, wherein thepermanent magnets are placed on the rotor between two pole body and poleshoe halves.

FIG. 2b is an approximate model schematic, representing the approximateflux producing capability of the rotor, in the hybrid machine of FIG. 2a.

FIG. 3 is a cross sectional schematic view of another embodiment ofhybrid machine according to the present disclosure.

FIG. 4 is a cross sectional schematic view of another embodiment ofhybrid machine according to the present disclosure.

FIG. 5 is a cross sectional schematic view of another hybrid machine.

FIGS. 6a-6d are a collection of plots of flux density vs. electricalangle relative to the rotor (Φ_(r)) for the hybrid machine of FIG. 2 a.

FIGS. 6a is a collection of plots of flux density vs. electrical anglerelative to the rotor for the hybrid machine of FIG. 2a , in accordancewith one or more embodiments.

FIGS. 6b is a collection of plots of flux density vs. electrical anglerelative to the rotor for the hybrid machine of FIG. 2a , in accordancewith one or more embodiments.

FIGS. 6c is a collection of plots of flux density vs. electrical anglerelative to the rotor for the hybrid machine of FIG. 2a , in accordancewith one or more embodiments.

FIGS. 6d is a collection of plots of flux density vs. electrical anglerelative to the rotor for the hybrid machine of FIG. 2a , in accordancewith one or more embodiments.

FIG. 7 is a block diagram of the components used in a power system todeliver power to a mechanical load in a motoring mode, or an electricalload in generating mode.

FIG. 8 is a plot of the loss vs. mass, for the hybrid machines accordingto the present disclosure and traditional PMSM and WRSM machines foundin the prior art.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of this disclosure is thereby intended.

A cross sectional schematic representation of one embodiment of a hybridsurface magnet (HSM) machine 100 according to the present disclosure isdepicted in FIG. 2a . The HSM 100 includes a stator assembly 102 and arotor assembly 103. The stator assembly 102 includes a stator backiron104 while the rotor assembly 103 includes a rotor backiron 105. Thestator assembly 102 further includes a distributed winding, configuredto provide a magnetomotive force (MMF) applicable on the rotor assembly103. The rotor assembly 103 is formed in the shape of a cylindricalbody, a rotational drive mechanism, in this case a shaft 125 positionedat the center of the rotor assembly 103, coupled to the rotor backiron105 by an inert rotor material 126 and configured to rotate along withthe rotor backiron 105, and a plurality of outwardly protrudedmagnetically permeable pole assemblies 121 which include field windings107 and one or more radially magnetized permanent magnets 108 whichtogether generate a magnetomotive force applicable on the statorassembly 103 and which together with the magnetomotive force generatedby the stator assembly 102 cause rotation of the rotor assembly 103. Thestator assembly 102 and the rotor assembly 103 are radially separated byan air gap 112. Each of the pole assemblies includes pole bodies 120 andpole shoes 122 surrounding the one or more permanent magnets 108 withspacers 127 between them.

The HSM 100 includes a conventional distributed winding based statorassembly 102. The stator assembly 102 includes a plurality of teeth 106inwardly protruded towards the center of the machine 100 along theradial direction, formed at predetermined intervals represented by slots111 along the circumferential direction. The stator assembly 102 isconfigured to have a winding that can be placed in the stator slots 111.

The flux from the rotor assembly 103 may be approximately modeled usinga parallel circuit configuration depicted in FIG. 2b . Based on themodel, a source identified as Ffd, referring to the magnetomotive forceassociated with the field windings 107 is in series coupling with aparallel network which includes another source identified as F_(pm),referring to the magnetomotive force associated with the one or morepermanent magnets 108, and further two reluctances

_(pm) and

_(g), referring to the permanent magnet and air gap. The magnetomotiveforce sources in the magnetic circuit, dissipated across thereluctances, produce a flux (Φ_(g)), similar to current in an electriccircuit comprised of electromotive force sources (i.e. voltage) andresistances. The source identified as F_(fd) terminates at a groundassociated with the rotor backiron 105 while the parallel network isterminated at a ground associated with the stator backiron 104. Thepercentage of the rotor pole 121 facing the air-gap 112 is representedby the factor α. The flux crossing the air-gap (Φ_(g)) is related totorque density.

The permanent magnets 108 allow the rotor assembly 103 to produce eithervoltage or torque with minimal losses as compared to those associatedwith excitation of the field winding 107. At higher loads in generatingmode, the field windings 107 are excited to account for the resultingvoltage drops and regulate the output. At higher loads in motoring mode,the field windings 107 are excited to produce additional flux, resultingin additional torque. At higher speeds (in both motoring and generatingmodes), the field windings 107 are excited in the reverse direction toprovide field weakening capability, allowing for power regulation. Theshape of the stator and rotor steel, as well as the placement of the MMFsources in the topologies explored allows the air-gap flux distributionto be manipulated, wherein the electromechanical energy conversionprocess occurs. Adequate placement of steel, magnets, spacers, andwindings allows the flux to be distributed such that the flux linkingthe stator winding is maximized.

Referring to FIG. 3, a cross sectional schematic representation ofanother embodiment of the HSM 200 is depicted. The HSM 200 includes astator assembly 202 and a rotor assembly 203. The stator assembly 202includes a stator backiron 204 while the rotor assembly 203 includes arotor backiron 205. The stator assembly 202 further includes a winding,configured to provide a magnetomotive force applicable on the rotorassembly 203. The rotor assembly 203 is formed in the shape of acylindrical body, a rotational drive mechanism, in this case a shaft 225positioned at the center of the rotor assembly 203, coupled to the rotorbackiron 205 by an inert rotor material 226 and configured to rotatealong with the rotor backiron 205, and a plurality of outwardlyprotruded magnetically permeable pole assemblies 221 which include fieldwindings 207 and one or more radially magnetized permanent magnets 208which together generate a magnetomotive force applicable on the statorassembly 203 and which together with the magnetomotive force generatedby the stator assembly 202 cause rotation of the rotor assembly 203. Thestator assembly 202 and the rotor assembly 203 are radially separated byan air gap 212. Each of the pole assemblies includes pole bodies 220 andpole shoes 222 surrounding the one or more permanent magnets 208 withspacers 227 between them.

Each of the plurality of poles assemblies 221 contains a T-shapedmagnetically permeable pole support assembly, which includes a pole body220 and a pole shoe 222, a radially magnetized permanent magnetassembly, which includes permanent magnets 208 and spacers 227, andfield winding 207 made of conductive materials. The permanent magnets208 are placed about the T-shaped pole support assembly, separated viathe spacers 227. The permanent magnets 208 are magnetized in the radialdirection. The field windings 207 is coiled around the pole supportassembly.

The permanent magnets 208 allow the rotor assembly 203 to produce eithervoltage or torque with minimal losses as compared to those associatedwith excitation of the field winding 207. At higher loads in generatingmode, the field windings 207 are excited to account for the resultingvoltage drops and regulate the output. At higher loads in motoring mode,the field windings 207 are excited to produce additional flux, resultingin additional torque. At higher speeds (in both motoring and generatingmodes), the field windings 207 are excited in the reverse direction toprovide field weakening capability, allowing for power regulation. Theshape of the stator and rotor steel, as well as the placement of the MMFsources in the topologies explored allows the air-gap flux distributionto be manipulated, wherein the electromechanical energy conversionprocess occurs. Adequate placement of steel, magnets, spacers, andwindings allows the flux to be distributed such that the flux linkingthe stator winding is maximized.

Referring to FIG. 4, a cross sectional schematic representation ofanother embodiment of the HSM 300 is depicted. The HSM 300 includes astator assembly 302 and a rotor assembly 303. The stator assembly 302includes a stator backiron 304 while the rotor assembly 303 includes arotor backiron 305. The stator assembly 302 further includes a winding,configured to provide a magnetomotive force applicable on the rotorassembly 303. The rotor assembly 303 is formed in the shape of acylindrical body, a rotational drive mechanism, in this case a shaft 325positioned at the center of the rotor assembly 303, coupled to the rotorbackiron 305 and configured to rotate along with the rotor backiron 305,and a plurality of outwardly protruded magnetically permeable poleassemblies 321 which include field windings 307 and one or more radiallymagnetized permanent magnets 308 which together generate a magnetomotiveforce applicable on the stator assembly 303 and which together with themagnetomotive force generated by the stator assembly 302 cause rotationof the rotor assembly 303. The stator assembly 302 and the rotorassembly 303 are radially separated by an air gap 312. Each of the poleassemblies includes pole bodies 320 and pole shoes 322 surrounding theone or more permanent magnets 308 with spacers 327 between them.

Each of the plurality of poles assemblies 321 contains a T-shapedmagnetically permeable pole support assembly, which includes a pole body320, a pole tip 323, and a pole shoe 322, a radially magnetizedpermanent magnet assembly, which includes permanent magnets 308 andspacers 327, and field winding 307 made of conductive materials. Thepermanent magnets 308 are placed about the T-shaped pole supportassembly, separated via the spacers 327. The permanent magnets 308 aremagnetized in the radial direction. The field winding 307 is coiledaround the pole support assembly.

The permanent magnets 308 allow the rotor assembly 303 to produce eithervoltage or torque with minimal losses as compared to those associatedwith excitation of the field winding 307. At higher loads in generatingmode, the field windings 307 are excited to account for the resultingvoltage drops and regulate the output. At higher loads in motoring mode,the field windings 307 are excited to produce additional flux, resultingin additional torque. At higher speeds (in both motoring and generatingmodes), the field windings 307 are excited in the reverse direction toprovide field weakening capability, allowing for power regulation. Theshape of the stator and rotor steel, as well as the placement of the MMFsources in the topologies explored allows the air-gap flux distributionto be manipulated, wherein the electromechanical energy conversionprocess occurs. Adequate placement of steel, magnets, spacers, andwindings allows the flux to be distributed such that the flux linkingthe stator winding is maximized.

FIG. 5 is a schematic view of yet another hybrid machine topology thatwas explored, containing a stator and two rotors mechanically coupledvia a common shaft, wherein a first rotor contains a backiron section, apole shoe, pole body, and field winding, and a second rotor containspermanent magnets on the surface of the rotor backiron. The topology isused, among others, to compare the relative benefits of the hybridmachine presented in this disclosure.

FIGS. 6a-6d are a collection of plots of flux density vs. electricalangle relative to the rotor (Φ_(r)) for the hybrid machine according toone embodiment of the present disclosure (see FIG. 2a ). The plottedflux densities are obtained using an analytical model (AM) and a finiteelement model (FEM), and include profiles resulting due to excitation ofthe a) q-axis, b) d-axis, c) field winding, and d) magnet. Typically, inthe analysis of electric machinery, the fringing flux, resulting in thecurved regions of a)-c), are ignored. For the hybrid machine HSM 100 ofthe present disclosure, ignoring the flux in these regions results ingenerally underestimating the associated flux linkages, and particularlythat resulting from the field winding, used to regulate the outputvoltage in generation mode, or allowing for an additional parameter toregulate output torque in motoring mode. As a result, the benefits ofthe embodiment of FIG. 2a , containing a magnet, with a lower relativepermeability than that of the rotor steel, in the center of the poleassembly 121, are not immediately obvious.

The hybrid machines HSM 100, 200, and 300 may be operated as part of anenergy conversion system shown in FIG. 7. Referring to FIG. 7, thesystem includes a mechanical arrangement that i) provides electricalpower in generation mode or ii) receives electrical power in motoringmode, a hybrid electrical machine, a power converter, a controller, aposition sensor (or estimator), and an electrical power i) load ingeneration mode or ii) source in motoring mode. The rotor position ofthe machine, the voltage and/or current at terminal t₁, and/or thevoltage and/or current at terminal t₂ are detected and used as afeedback to the controller to determine the appropriate field windingvoltage and/or current. A position estimator can also be used toestimate position of the rotor and use the estimated position of therotor as a feedback signal in a similar manner.

Referring to FIG. 7, the system operating in power generation modeincludes an electrical load, which is one of a single-phase alternatingpower load, a multi-phase alternating power load, a direct current powerload, and other loads known to a person having ordinary skill in theart.

Referring to FIG. 7, the system operating in motoring mode includes anelectrical power source, which is one of a single-phase alternatingpower source, a multi-phase alternating power source, a direct currentpower source, and other sources known to a person having ordinary skillin the art.

Referring to FIG. 7, the power converter may be operating in AC/AC modeor AC/DC mode, with one AC side coupled to the electrical connection ofthe hybrid electrical machine. The converter is comprised of a pluralityof switching devices, which may be of various types, including passiveswitches (e.g. diodes), semi-active switches (e.g. thyristors), andactive switches (e.g. IGBTs). If semi-active or active switches areused, a controller is configured to provide the required controlsignals.

In FIG. 8, the Pareto-optimal fronts, providing the mass vs. losscharacteristic, known to a person of ordinary skill in the art, ofseveral hybrid machine topologies, as well as of a WRSM and PMSM, areshown. Each machine topology is optimized to minimize loss and mass fora given output power. The computation of this characteristic is repeatedtwice for each machine to check for consistency. From the Pareto-optimalfront comparison in FIG. 8, the HSM 100 topology (referred in the figureas parallel-inner-split) is shown to have a better tradeoff than theWRSM and comparable to that of a PMSM.

Those skilled in the art will recognize that numerous modifications canbe made to the specific implementations described above. Therefore, thefollowing claims are not to be limited to the specific embodimentsillustrated and described above. The claims, as originally presented andas they may be amended, encompass variations, alternatives,modifications, improvements, equivalents, and substantial equivalents ofthe embodiments and teachings disclosed herein, including those that arepresently unforeseen or unappreciated, and that, for example, may arisefrom applicants/patentees and others.

The invention claimed is:
 1. A machine comprising: a rotor assembly concentrically disposed within a stator assembly, the rotor assembly comprising a rotor backiron; a drive mechanism coupled to the rotor backiron and configured to rotate in association with the rotor backiron, and a plurality of rotor poles, each rotor pole comprising a pole support assembly, a winding provided around the pole support assembly, and a magnet assembly disposed about the pole support assembly, wherein the pole support assembly includes a T-shaped pole support, and wherein the magnet assembly comprises a plurality of permanent magnets, wherein each permanent magnet of the plurality of permanent magnets is on each side of the T-shaped pole support, wherein the each permanent magnet of the plurality of permanent magnets is not in physical contact with the T-shaped pole support.
 2. The machine of claim 1, further comprising a spacer between each permanent magnet of the plurality of permanent magnets and the T-shaped pole support.
 3. The machine of claim 1, wherein the T-shaped pole support includes side bars.
 4. The machine of claim 1, wherein the rotor backiron is in a shape of a cylindrical body.
 5. A machine comprising: a rotor assembly concentrically disposed within a stator assembly, the rotor assembly comprising a drive mechanism coupled to a rotor backiron, and a plurality of rotor poles, wherein each rotor pole comprises a magnet assembly disposed about a pole support assembly, wherein the pole support assembly includes a T-shaped pole support, and wherein the magnet assembly comprises a plurality of permanent magnets, wherein each permanent magnet of the plurality of permanent magnets is on each side of the T-shaped pole support, wherein the each permanent magnet of the plurality of permanent magnets is physically disjointed with the T-shaped pole support.
 6. The machine of claim 5, further comprising a spacer between each permanent magnet of the plurality of permanent magnets and the T-shaped pole support.
 7. The machine of claim 5, wherein the drive mechanism is configured to rotate in association with the rotor backiron.
 8. The machine of claim 5, wherein the rotor backiron is in a shape of a cylindrical body.
 9. The machine of claim 5, further comprising a winding around the pole support assembly.
 10. The machine of claim 5, wherein the T-shaped pole support includes side bars.
 11. A machine comprising: a rotor assembly disposed within a stator assembly, wherein the rotor assembly comprises: a rotational drive mechanism coupled to a rotor backiron, and a plurality of rotor poles, wherein each rotor pole comprises a pole support assembly, wherein the pole support assembly comprises a pole body and a pole shoe, wherein the pole shoe comprises a plurality of recesses, and a plurality of permanent magnets, wherein each permanent magnet of the plurality of permanent magnets is over each recess of the plurality of recesses of the pole shoe.
 12. The machine of claim 11, further comprising a spacer between each permanent magnet of the plurality of permanent magnets and a sidewall of a respective recess of the plurality of recesses.
 13. The machine of claim 11, wherein the drive mechanism is configured to rotate in association with the rotor backiron.
 14. The machine of claim 11, wherein the rotor backiron is in a shape of a cylindrical body.
 15. The machine of claim 11, further comprising a winding around the pole support assembly. 